10. Security Considerations

OpenLDAP Software is designed to run in a wide variety of computing environments from tightly-controlled closed networks to the global Internet. Hence, OpenLDAP Software supports many different security mechanisms. This chapter describes these mechanisms and discusses security considerations for using OpenLDAP Software.

By default, slapd(8) will listen on both the IPv4 and IPv6 "any" addresses. It is often desirable to have slapd listen on select address/port pairs. For example, listening only on the IPv4 address 127.0.0.1 will disallow remote access to the directory server. E.g.:

slapd -h ldap://127.0.0.1

While the server can be configured to listen on a particular interface address, this doesn't necessarily restrict access to the server to only those networks accessible via that interface. To selective restrict remote access, it is recommend that an IP Firewall be used to restrict access.

slapd(8) supports TCP Wrappers. TCP Wrappers provide a rule-based access control system for controlling TCP/IP access to the server. For example, the host_options(5) rule:

slapd: 10.0.0.0/255.0.0.0 127.0.0.1 : ALLOW
slapd: ALL : DENY

allows only incoming connections from the private network 10.0.0.0 and localhost (127.0.0.1) to access the directory service. Note that IP addresses are used as slapd(8) is not normally configured to perform reverse lookups.

It is noted that TCP wrappers require the connection to be accepted. As significant processing is required just to deny a connection, it is generally advised that IP firewall protection be used instead of TCP wrappers.

Transport Layer Security (TLS) can be used to provide data integrity and confidentiality protection. OpenLDAP supports negotiation of TLS (SSL) via both StartTLS and ldaps://. See the Using TLS chapter for more information. StartTLS is the standard track mechanism.

A number of Simple Authentication and Security Layer (SASL) mechanisms, such as DIGEST-MD5 and GSSAPI, also provide data integrity and confidentiality protection. See the Using SASL chapter for more information.

The server uses Security Strength Factors (SSF) to indicate the relative strength of protection. A SSF of zero (0) indicates no protections are in place. A SSF of one (1) indicates integrity protection are in place. A SSF greater than one (>1) roughly correlates to the effective encryption key length. For example, DES is 56, 3DES is 112, and AES 128, 192, or 256.

A number of administrative controls rely on SSFs associated with TLS and SASL protection in place on an LDAP session.

security controls disallow operations when appropriate protections are not in place. For example:

Anonymous access is requested by providing no name and no password to the "simple" bind operation. Unauthenticated access is requested by providing a name but no password. Authenticated access is requested by providing a valid name and password.

An anonymous bind results in an anonymous authorization association. Anonymous bind mechanism is enabled by default, but can be disabled by specifying "disallow bind_anon" in slapd.conf(5). Note that disabling the anonymous bind mechanism does not prevent anonymous access to the directory. To require authentication to access the directory, one should instead specify "require authc".

An unauthenticated bind also results in an anonymous authorization association. Unauthenticated bind mechanism is disabled by default, but can be enabled by specifying "allow bind_anon_cred" in slapd.conf(5). As a number of LDAP applications mistakenly generate unauthenticated bind request when authenticated access was intended (that is, they do not ensure a password was provided), this mechanism should generally remain disabled.

A successful user/password authenticated bind results in a user authorization identity, the provided name, being associated with the session. User/password authenticated bind is enabled by default. However, as this mechanism itself offers no evesdropping protection (e.g., the password is set in the clear), it is recommended that it be used only in tightly controlled systems or when the LDAP session is protected by other means (e.g., TLS, IPSEC). Where the administrator relies on TLS to protect the password, it is recommended that unprotected authentication be disabled. This is done using the security directive's simple_bind option, which provides fine grain control over the level of confidential protection to require for simple user/password authentication. E.g., using security simple_bind=56 would require simple binds to use encryption of DES equivalent or better.

The user/password authenticated bind mechanism can be completely disabled by setting "disallow bind_simple".

Note: An unsuccessful bind always results in the session having an anonymous authorization association.